Xilinx Spartan 3e Starter Kit
Of particular interest to people interested in building synthesisers with FPGAs is the fact that this board has everything on you need, a BIG FPGA, fast clock, lots of memory and most importantly a DAC!
Most people on the list seem to have one of these boards to hand, so I'd expect that this will quickly become the standard weapon of choice for projects/code contained in this wiki. Though I'll try to keep it as open and free from constraints as possible.
You can get more info, and buy direct, from the XilinX page - http://www.xilinx.com/xlnx/xebiz/designResources/ip_product_details.jsp?key=HW-SPAR3E-SK-US